Fingerprint sensor pattern

ABSTRACT

An example system drives one or more transmit signals on first electrodes disposed in a first layer and propagating electrodes disposed in a second layer. The system measures a capacitance of sensors through a of second electrodes. Each second electrode crosses each first electrode to provide a plurality of discrete sensor areas, each discrete sensor area associated with a difference crossing and including a portion of at least one propagating electrode. Each second electrode is galvanically isolated from the first electrodes and the propagating electrodes.

RELATED APPLICATIONS

This application is Continuation Application of U.S. Non provisionalapplication Ser. No. 14/977,267, filed Dec. 21, 2015, which claims thepriority benefit of U.S. Provisional Application No. 62/216,924, filedSep. 10, 2015, all of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The subject matter relates to the field of biometric sensors. Morespecifically, but not by way of limitation, the subject matter disclosesarrangements of fingerprint sensor patterns.

BACKGROUND

Capacitance sensing systems function by sensing electrical signalsgenerated on electrodes that represent changes in capacitance. Suchchanges in capacitance can indicate the presence of ridges and valleysof a fingerprint. Fingerprint sensing may be used for security andvalidation applications for a variety of user interface devices, such asmobile handsets, personal computers, and tablets. The use of capacitancesensing for fingerprint detection may allow for a sensor to be placed inthe surface of a user interface device with a great degree ofconfigurability. That is, a sensor is not constrained to a singlelocation for all devices. Rather, a fingerprint sensor may be disposedin a location on the device that is convenient for a particularindustrial design, or to optimize a user's experience.

Capacitance-based fingerprint sensors function by measuring thecapacitance of a capacitive sense element, such as a sensor electrode,and detecting a change in capacitance indicating a presence or absenceof a fingerprint ridge (or valley). Ridges and valleys at identifiablelocations on an array of sense elements may be used to reconstruct theimage of the fingerprint for use in enrollment, validation, and securityapplications. When a fingerprint ridge comes into contact with or is inclose proximity to a sense element, the capacitance change caused by thefingerprint ridge is detected. The capacitance change of the senseelements can be measured by an electrical circuit that converts thecapacitances measured from the capacitive sense elements into digitalvalues.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which:

FIG. 1 is a block diagram illustrating a fingerprint sensing system, inaccordance with various embodiments;

FIG. 2 is a block diagram illustrating layers of a fingerprint module,in accordance with various embodiments;

FIG. 3 is a block diagram illustrating a plan view of a sensor array, inaccordance with embodiments;

FIG. 4 is a block diagram illustrating a cross-sectional view of asensor array, in accordance with an embodiment;

FIG. 5 is a block diagram illustrating a cross sectional view of asensor array, in accordance with an embodiment;

FIG. 6 is a chart diagram illustrating a propagating electrode's effecton capacitance in response to a fingerprint feature, in accordance withembodiments;

FIG. 7 is a chart diagram including sensor signal results with andwithout the use of rectangular propagating electrodes, in accordancewith embodiments;

FIG. 8 show a plan view of a sensor array, in accordance withembodiments;

FIG. 9 shows a plan view of a sensor array, in accordance withembodiments;

FIG. 10 shows a plan view of a sensor array, in accordance withembodiments;

FIG. 11 shows a plan view of a sensor array, in accordance withembodiments;

FIG. 12 is a block diagram illustrating an electronic system, inaccordance with embodiments; and

FIG. 13 is a block diagram illustrating a sensor array and a capacitancesensor, in accordance with embodiments.

DETAILED DESCRIPTION

Fingerprint sensor patterns are described. In the following description,for purposes of explanation, numerous examples are set forth in order toprovide a thorough understanding of the embodiments. It will be evidentto one skilled in the art that the claimed subject matter may bepracticed in other embodiments. The detailed description disclosesexamples of fingerprint sensor patterns including electrodes arranged invarious patterns and layers, which when energized, provide an enhancedresponse to fingerprint features proximate to the electrodes compared toexisting arrangements.

Some embodiments are now briefly introduced and then discussed in moredetail along with other embodiments beginning with FIG. 1. In anembodiment, a fingerprint module provides multiple capacitive sensorsused by a processing device to detect fingerprint features. Thecapacitive sensors can be constructed on a substrate from multiplelayers, including but not limited to, a layer including transmit (TX)electrodes, a layer including receive (RX) electrodes and propagatingelectrodes, and a layer including insulating material to galvanicallyisolate the TX electrodes from the RX electrodes. An overlay material tocover and/or protect the capacitive sensors may be placed above the RXelectrodes.

In an embodiment, the TX electrodes (e.g., rows of TX electrodes), theRX electrodes (e.g., columns of RX electrodes), and propagatingelectrodes are arranged in a pattern in which each TX electrodeintersects (e.g. crosses) each RX electrode. The intersections form arepeating unit (e.g., a unit cell) of the pattern that can define theresolution of the fingerprint module. The unit cells correspond todiscrete locations where a processing device can resolve a fingerprintfeature. Each capacitive sensor corresponds to a unit cell, and includesan intersection between a TX electrode and an RX electrode, and at leasta portion of a propagating electrode. The processing device can measureeach capacitive sensor to detect a fingerprint feature proximate to thecapacitive sensor. To measure a capacitive sensor, the electricpotential of the TX electrode is coupled to the propagating electrodeand the RX electrode and the processing device receives a resultingsensor signal from the RX electrode. When a fingerprint feature isproximate to a capacitive sensor, the sensor signal includes a signalcomponent that indicates a change in capacitance of the RX electrodecaused by the proximity of the fingerprint feature. The sensor signalmay also include noise components and other components that are notuseful for fingerprint feature detection. The processing device can thengenerate an image of a fingerprint based on the fingerprint featuresdetected at the multiple capacitive sensors.

The physical and electrical relationships between TX electrodes, RXelectrodes, propagating electrodes, insulating material, overlaymaterial and other components, as well as their individual attributes,determine the capacitance change of a capacitive sensor indicated on theRX electrode in response to a proximate fingerprint feature. Theserelationships and attributes also determine the level of uniformity insignal response (e.g., the level of anisotropy) to fingerprint featurespresented at different angles relative to the RX electrode, for example,of the capacitive sensor. The TX potential will affect the change incapacitance of the capacitive sensor caused by the fingerprint featureand injected noise will affect the signal-to-noise ratio (SNR) of thesensor signal. Increasing coverage of the substrate by TX electrodes(e.g., minimizing deletions between TX electrodes) may increasinglyshield noise from being injected into the sensor signal (e.g., by systemelements opposite the TX electrodes from the RX electrodes). Thus,different attributes of the TX electrodes, insulating material,propagating electrodes, RX electrodes and/or overlay material andrelationships (e.g., physical and electrical) between these componentsmay be applied in various combinations, per capacitive sensor, andadjusted to design capacitive sensors that meet targeted sensor signallevels at acceptable SNR and anisotropy.

In configurations without the propagating electrodes, the insulatingmaterial and the overlay, depending on their thicknesses and materialproperties, can reduce the sensitivity of the capacitive sensors suchthat their sensor signals do not allow accurate fingerprint featuredetection. The fingerprint sensor patterns and arrangements describedherein use propagating electrodes to increase the change in capacitanceof capacitive sensors caused by the proximity of a fingerprint feature(oriented in any direction) to the capacitive sensors. This increases auseful component of the sensor signal, the SNR of the sensor signal, andthe anisotropy of the sensor signal, which result in more accuratefingerprint feature detection, fingerprint image generation, andfingerprint authentication.

In an example embodiment of a fingerprint sensor pattern multiple TXelectrodes disposed in a first layer cross with multiple RX electrodesdisposed in a second layer. In this embodiment, the second layer iscloser to the fingerprint input surface than the first layer. Multiplepropagating electrodes are disposed in the second layer along with themultiple RX electrodes. In a plan view of the fingerprint sensorpattern, an area of each propagating electrode is located within an areaof each TX electrode. In the second layer, each RX electrode is disposedbetween two or more of the multiple propagating electrodes. Each RXelectrode is also galvanically isolated from each propagating electrodeand each TX electrode. Each RX electrode and propagating electrodecouples with the TX signal. The propagating electrodes may becapacitively or conductively coupled with the TX signal. When coupledwith the TX signal, the propagating electrodes hold electric potentialof the TX electrodes in the second layer and capacitively couple withthe RX electrodes. Each capacitive sensor of the fingerprint sensorpattern comprises an intersection between a TX electrode and an RXelectrode and comprises at least a portion of a propagating electrode.

When a fingerprint feature capacitively couples with a propagatingelectrode, it shunts charge from an RX electrode, resulting in anincreased change in capacitance of the capacitive sensor compared toembodiments without propagating electrodes. This increases the usefulcomponent of the sensor signal, the SNR of the sensor signal, and theanisotropy of the sensor signal, which can result in the more accuratefingerprint feature detection, fingerprint image generation, andfingerprint authentication. Further embodiments are described herein.

The detailed description below includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow illustrations in accordance with embodiments. These embodiments,which are also referred to herein as “examples,” are described in enoughdetail to enable those skilled in the art to practice embodiments of theclaimed subject matter. The embodiments may be combined, otherembodiments may be utilized, or structural, logical, and electricalchanges may be made without departing from the scope of what is claimed.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope is defined by the appended claims andtheir equivalents.

FIG. 1 is a block diagram illustrating a fingerprint sensing system 100in accordance with various embodiments. The fingerprint sensing system100 includes fingerprint module 104 and a processing device 106. Thefingerprint module 104 includes a surface 105 (e.g., and overlay) toreceive a fingerprint from a finger 110 which may coincide with anactive area under which capacitive sensors may experience changescapacitances in response to the proximity of fingerprint features of thefinger 110. The fingerprint module 104 and/or its active area may be inthe shape of a square, rectangle, circle, or any other shape, withoutdeparting from the claimed subject matter. In an embodiment, fingerprintfeatures may include, but not be limited to, valleys and ridges formingarches, loops, and whorls.

The processing device 106 is to scan the capacitive sensors for sensorsignals representing the changes in a capacitance and then use thosesignals to generate a fingerprint image 112. As used herein,“fingerprint image” refers to a set of data values (e.g., fingerprintdata) that represents a fingerprint in digital format. In someembodiments, a fingerprint image may be a dataset that visuallyrepresents the valleys and ridges of a fingerprint with their arches,loops, and whorls. In other embodiments, a fingerprint image may be adataset that digitally represents a fingerprint in a non-visual form.For example, a data structure with data values from which a visualrepresentation of the fingerprint may be obtained after furtherprocessing or which may be used by various fingerprint processingoperations.

The fingerprint sensor system's 100 ability to acquire and processfingerprint image data overcomes unique challenges that are notnecessarily (if at all) addressed by techniques developed for typicaltouch sensing. The structure and operation of the fingerprint sensingsystem 100 differs from other, common sensor modules (e.g., such astouch-screen sensor modules) in at least several aspects. For example,the active area of the fingerprint module 104 may be one to two ordersof magnitude (e.g., about 100 times) smaller than the active area of atypical touch-screen sensor module. In an embodiment, the fingerprintmodule 104 is designed such that the finger 110 covers the majority(e.g., more than 75%) of its active area. In various embodiments, theactive area of the fingerprint module 104 is in the range from 4×4 mm to12×12 mm. For a typical capacitive touch (e.g., touch-screen) sensormodule (e.g., on a smartphone), a contact from a single conductiveobject (e.g., user's finger or a stylus) typically covers only a smallfraction of the touch-screen active area and the active area may bearound 50×100 mm (and even larger active areas for tablets andlaptop/notebook computers).

The number of capacitive fingerprint sensors (e.g., 14,000) that may beused in the fingerprint module 104 is significantly larger than thenumber of capacitive touch sensors (e.g., 200) that may be used in atouch-screen sensor module. Further, the change in capacitance (e.g.,0.05 fF) that may be measured in a fingerprint sensing system 100 todetect a fingerprint feature is significantly smaller than the change incapacitance (e.g., 300 fF) that may be used by typical touch-screensystems to detect a touch. Thus, fingerprint sensing system 100 must besensitive and manage or avoid noise signals in order to capture a usablefingerprint image.

The fingerprint module 104, including its surface 105 and capacitivesensors, may be constructed from multiple layers of material. Examplelayers associated with the fingerprint module 104 are discussed withrespect to FIG. 2. FIG. 2 is a block diagram illustrating layers of afingerprint module 204, in accordance with various embodiments. Thesubstrate 206 may serve as a foundation and electrical insulator forlayers and/or components coupled directly or indirectly to its surface.In embodiments, the substrate 206 may include a ball grid arraysubstrate, a flexible or rigid printed board or any material orcombination of materials suitable for providing sufficient foundationand electrical insulation. In an embodiment, the processing device 104of the fingerprint sensing system 100 is coupled to the substrate (e.g.,on a same side or a different side than other components) and may be asource of noise that affects the SNR of sensor signals.

On top of the substrate 206 is shown a layer including TX electrodes208, a layer including an insulating material 210, a layer including RXelectrodes and propagating electrodes 214, and a layer including anoverlay material 216. Other embodiments of the fingerprint module 204may include a greater or fewer number of layers to provide thecomponents of the layers (e.g., the TX electrodes 208, the insulatingmaterial 210, the RX electrodes 212, the propagating electrodes 214, andthe overlay material 216) and/or additional components (not shown).Other embodiments may also provide the components using a differentorder of layers or by combining one or more of the components in commonlayers. Alternatively or additionally, some components may be providedin more than one layer.

The TX electrodes 208 capacitively couple with the RX electrodes 212 toform the capacitive sensors. The insulating material 210 serves toisolate the TX electrodes 208 from the RX electrodes 212, and thepropagating electrodes 214. The isolation of the TX electrodes 208 fromthe RX electrodes 212 is galvanic. In some embodiments, the isolation ofthe TX electrodes 208 from the RX electrodes 212 is galvanic. Theinsulating material 210 may include any dielectric material suitable fortarget capacitance ranges of a particular fingerprint sensingapplication. The insulating material 210 may include a layer ofadhesive, epoxy or be provided by the resin in a layer of a PCB. In anembodiment, the more electrically insulative the insulating material210, the less electromagnetic fields from the TX electrodes are able tocarry the TX potential to the layer including the RX electrodes 212 andthe propagating electrodes 214. In an embodiment, propagating electrodes214 electrically couple with the TX electrodes to carry the TX electricpotential to the layer including the RX electrodes 212. As furtherdiscussed below, this increases the effect of a proximate fingerprintfeature on the capacitance of a capacitive sensor.

The TX electrodes 208, RX electrodes 212, and propagating electrodes 214are formed from conductive material and may be disposed in theirrespective layers, like the insulating material 210 and overlay 216,through deposition, coating, material removal, patterning, and/or otherelectronic device fabrication techniques. The transparency or visibilityof the selected conductive material may vary in different embodiments,without departing from the claimed subject matter. In variousembodiments, one or more of the TX electrodes 208, RX electrodes 212,and the propagating electrodes 214 may be formed from metal (e.g.,copper traces), indium tin oxide, or other conductive material on orwithin one or more layers of a thin film, PCB, glass, or other material.The TX electrodes 208, RX electrodes 212, and the propagating electrodes214 may be also be implemented as chip on glass. Example sensor arraysbased on TX electrodes, RX electrodes, and propagating electrodes arefurther discussed below beginning with the discussion of FIG. 3.

The overlay material 216 is to cover and/or protect the underlyingcomponents from direct physical contact by a finger or other objects.The thickness and durability of the overlay material 216 may be selectedfor different applications and/or to withstand contact by fingers andother objects for a service life. In some embodiments, the thicker theoverlay material 216 covering the capacitive sensors, the less sensitivethe capacitive sensors become (e.g., the less a proximate fingerprintfeature can change the capacitance of a capacitive sensor). In someembodiments, the thickness of the overlay material 216 is thicker than apitch of the TX electrodes and/or the RX electrodes. In an embodiment,the increased sensor sensitivity and reduced anisotropy provided by thepropagating electrodes 214 can offset the negative effect of the overlaymaterial 216. In various embodiments, the overlay material 216 may beglass, ceramic, crystal sapphire, kapton tape, or other materialssuitable to the system design parameters. The level of conductivity ofthe overlay material, for a given thickness, can also affect sensorsensitivity (e.g., negatively or positively). In some embodiments, theoverlay material 216 is between 100 um and 250 um thick. The overlaymaterial 216 may be thinner than 100 um or thicker than 250 um in otherembodiments.

Through the embodiments described herein, the physical arrangement ofthe TX electrodes, RX electrode, and propagating electrodes may beoptimized to achieve target sensor performance including sensitivity tofingerprint features, SNR, anisotropic response level (e.g., the degreeof uniformity of signal response to fingerprint features varying inangle relative to the RX electrodes and/or TX electrodes). Examplearrangements of these fingerprint sensor component s are described withrespect to FIGS. 3-11.

FIG. 3 is a block diagram illustrating a plan view of a sensor array 300(e.g., a capacitive fingerprint sensor array), in accordance withembodiments. The sensor array 300 includes TX electrodes 302 crossing(e.g., intersecting) with RX electrodes 320. Each unit cell (e.g., theunit cell 360) at (e.g., centered on) each intersection between a TXelectrode 302 and an RX electrode 320 corresponds to a fingerprintcapacitive sensor.

In the embodiments described herein, a capacitive sensor may correspondto a unit cell. The unit cell 360 includes an area where a TX electrode302 and a propagating electrode 340 capacitively couple to an RXelectrode 320 and where the capacitance can be measured through the RXelectrode 320. The unit cell 360 is shown to be square in shape but theunit cell 360 (e.g., and corresponding capacitive sensor) may be shapeddifferently without departing from the claimed subject matter. For easeof illustration, sensor array 300 shows only a portion of the totalnumber of TX electrodes 302 and RX electrodes 320 that may be used inthe fingerprint module 104 of FIG. 1. In some embodiments, the number ofRX electrodes 320 and TX electrodes 302 may range from 100 to 150 each,resulting in 10,000 or more measurable capacitive sensors. A pitch ofthe capacitive sensors may be less than 100 um (e.g., 70 um) and in someembodiments, the pitch is selected such that each fingerprint featureplaced on the fingerprint sensor can be detected by at least threecapacitive sensors.

In the plan view of the sensor array 300, the area of each propagatingelectrode 340 is positioned above an area of a TX electrode 302, and anarea of each TX electrode 302 is positioned below an area of apropagating electrode 340. The partial or total area consumed by eachpropagating electrode 340, as shown in the plan view, may be locatedwithin the area of a corresponding TX electrodes 302 and betweenadjacent RX electrodes 320. The area of each unit cell 360 and/or thecorresponding capacitive sensor may overlap with the area of apropagating electrode 340. In some embodiments, a total area of apropagating electrode 340 may overlap with the area of a unit cell 360(e.g., see FIG. 11) and/or the corresponding capacitive sensor.

The propagating electrodes 340 are shown to be spaced apart from oneanother along a TX electrode 302, with an RX electrode 302 disposedbetween and adjacent to two propagating electrodes 340, the patternalternating between propagating electrodes 340 and RX electrodes. Inother embodiments, RX electrodes 320 may be disposed between more thantwo propagating electrodes 320 or more than one RX electrode 320 may bedisposed between propagating electrodes 340. The propagating electrodes340 over each TX electrode 302 are shown to be aligned along an axis(not shown) of that TX electrode 302. In an embodiment, this axisintersects only the corresponding TX electrode 302 (e.g., at themidpoint of its width 324) and is parallel to the X-axis of the XY axes301 (e.g., a horizontal axis). Propagating electrodes 340 over differentTX electrodes 302 are shown to be aligned along an axis (not shown) thatintersects multiple different TX electrodes 302. In an embodiment, thisaxis is parallel to the Y-axis of the X-Y axis 301 (e.g., a verticalaxis). As will be described in further detail below, various shapes,sizes, locations, and other attributes of propagating electrodes 340 maybe employed in a sensor array, without departing from the claimedsubject matter.

The TX electrodes 302, having the width 306, are shown to be spacedapart according to pitch 304. The amount of space between each TXelectrode 302 (e.g., a deletion) is defined by the pitch 304 minus thewidth 306. The RX electrodes 320, having the width 324, are shown to bespaced apart according to the pitch 322. The propagating electrodes 340,having the width 342, are shown to be equally spaced apart but theirspacing, TX electrode pitch, and RX electrode pitch may not be constantacross a sensor array in various embodiments.

In an embodiment, the width 306 of one or more of the TX electrodes 302is greater than half the pitch 304 and the width 324 of one or more ofthe RX electrodes 320 is less than half of the pitch 322. In someembodiments, the thickness of the overlay material is greater than apitch of the TX electrodes 302 and/or the RX electrodes 320. The widthof the unit cell 360 may be equal to the pitch 304 and/or the pitch 322.The width 342 of each propagating electrode 342 may be substantially thesame (e.g., subject to selected manufacturing tolerances) as the width324 of the RX electrodes 320. In embodiments, the greater the ratiobetween the pitch 304 and the width 306 of the TX electrodes 302, themore the TX electrodes 302 can shield the capacitive sensors from noiseinjected by noise sources (e.g., a processing device) located nearby(e.g., coupled to the substrate below the TX electrodes 302). Wider TXelectrodes 302 may also strengthen capacitive coupling to the RXelectrodes 320 and the propagating electrodes 340. Such noise shieldingand strengthened capacitive coupling may result in a higher overallsignal response (e.g., useful component of sensor signal) and SNR. Insome embodiments, the width 306 of the TX electrodes 302 is between 20um and 65 um and the width 324 of each RX electrode 320 and propagatingelectrode 340 is between 5 um and 15 um. The TX electrodes 302 and theRX electrodes 320 may be made of non-transparent metal material and havethe same pitch in the range of 40 um to 80 um.

As introduced above, to increase the effect of a proximate fingerprintfeature on the capacitance of a capacitive sensor (e.g., correspondingto a unit cell), the propagating electrodes 340 electrically couple withthe TX electrodes 302 to carry the electric potential of the TXelectrodes to the layer including the RX electrodes 320. FIGS. 4 and 5illustrate embodiments for electrically coupling the propagatingelectrodes 340 to the TX electrodes 302.

FIGS. 4 and 5 are block diagrams illustrating a cross-sectional view(along the section A-A) of different embodiments of the sensor array 300of FIG. 3. FIG. 4 shows a cross-sectional view of a sensor array 400including insulating material 410 disposed between a TX electrode 402 onthe bottom and propagating electrodes 440 and RX electrodes 420 on thetop. In this embodiment, the insulating material 410 galvanicallyisolates the TX electrodes 402 from the propagating electrodes 440. TheTX electrodes 402 may then capacitively couple with the propagatingelectrodes 440 to carry electrical potential of the TX electrodes 402 upto the same layer as the RX electrodes 420.

Similarly, FIG. 5 shows a cross-sectional view of a sensor array 500including an insulating material 510 disposed between TX electrode 502on the bottom and propagating electrodes 540 and RX electrodes 520 onthe top. In this embodiment, conductive members 560 (e.g., metal traces)conductively couple the TX electrodes 402 to the propagating electrodes440 to provide the electrical potential to the same layer as the RXelectrodes 520. The conductive members 560 may be provided in via holesthrough the insulating material 510, or by any other common routingtechniques to transferring the electrical potential of the TX electrodes(e.g., the TX potential) closer to the surface 105 of the fingerprintmodule 104 of FIG. 1. Providing this electric potential where thefingerprint features of the finger 110 are closest, increases the effectof a proximate fingerprint feature on the change of capacitance of thecapacitive sensors, resulting in increased SNR.

FIG. 6 is a chart diagram illustrating propagating electrode effect oncapacitance in response to a fingerprint feature, in accordance withembodiments. FIG. 6 shows the cases where no propagating electrode ispresent 601 in a capacitive sensor, a floating propagating electrode ispresent 603 in a capacitive sensor, and coupled propagating electrode ispresent 605 in a fingerprint capacitive sensor. For ease of explanation,the measurement of capacitive sensor of each case (601, 603, and 605) isdiscussed with respect to the middle RX electrode of the three RXelectrodes. The number of field lines pointing to the fingerprintfeatures 650 is proportional to the amount of electric potentialavailable on the propagating electrodes in the same layer as the RXelectrodes. The greater the electric potential in the same layer as theRX electrodes, the greater the capacitance between fingerprint featuresand the propagating electrodes of the capacitive sensor. Thus, the morefield lines pointing to the fingerprint features 650, the greater thechange in capacitance of the capacitive sensor caused by the fingerprintfeatures 650.

The case of no propagating electrode present 601 generates the fewestnumber of field lines between the capacitive sensor 670 (e.g., includingthe TX electrode 602, and the middle RX electrode 620) and thefingerprint features 650 because the potential difference between thetwo is the lowest of the three cases.

In the case where the floating propagating electrodes are present 603,the potential difference between capacitive sensor 675 and thefingerprint features 650 increases with the propagating electrodes 440capacitively coupled with the TX electrode 402. In this embodiment, thecapacitance between the TX electrode 402 and the propagating electrodes440 is greater than the capacitance between the TX electrode 402 and themiddle RX electrode 420. The case where the floating propagatingelectrodes are present 603 generates a greater number of field linesbetween the capacitive sensor 675 and the fingerprint features 650 thanthe case where no propagating electrodes are present 601. Thus, thecapacitance between fingerprint features 650 and the propagatingelectrodes 440 of the capacitive sensor 675 is greater than thecapacitance between the fingerprint feature 650 and the capacitivesensor 670.

In the case where the coupled propagating electrodes are present 605,the potential difference between the capacitive sensor 680 and thefingerprint features 650 further increases with the direct conductivepath between the propagating electrodes 540 and the TX electrode 502provided by the conductive members 560. As a result, the case in whichthe coupled propagating electrodes are present 605 yields the greatestsensor sensitivity because this case generates the greatest number offield lines between the capacitive sensor and the fingerprint features650 out of all three cases. The capacitance between fingerprint features650 and the propagating electrodes 540 of the capacitive sensor 680 isgreater than the capacitance between the fingerprint features and thecapacitive sensors in the cases 601 and 603, discussed above. Thus thechange of capacitance of the capacitive sensor 680 of case 605, asmeasured on the middle RX electrode 520 is greater than the change incapacitance of the capacitive sensors 670 and 675 of case 601 and case603, respectively.

FIG. 7 is a chart diagram including sensor signal results with andwithout the use of rectangular propagating electrodes, in accordancewith embodiments. Sensors arrays with a 25 um thick insulating layer anda 40 um thick insulating layer were tested. Sensor arrays with each ofthese insulating layer thicknesses were separately tested with nopropagating electrode and rectangular propagating electrodes sized at 30um×60 um, 15 um×50 um, and 30 um×15 um, respectively. For each test, thesensor signals in response to ridges parallel to RX electrodes andridges parallel to TX electrodes were measured and are shown in FIG. 7in units of femtofarads. The results illustrate the increased sensorsignal values that result from the use of propagating electrodes as wellas the effect that shape, size, and position of propagating electrodesmay have on the level of isotropic signal response.

As illustrated in the embodiments, the attributes of size, shape,arrangement, number, and/or material composition of TX electrodes,insulating material layer, propagating electrodes, RX electrodes and/oroverlay material, per capacitive sensor, can affect the capacitancebetween TX electrodes and the propagating electrodes, the direction ofelectric field lines to the propagating electrodes, and/or the overallamount of TX potential transferred to the propagating electrodes.Furthermore, the attributes of the TX electrodes, insulating layer,propagating electrodes, RX electrodes and/or overlay material, percapacitive sensor, can affect the capacitances between the TX electrodesand RX electrodes as well as the capacitances between RX electrodes andpropagating electrodes.

The physical and electrical relationships between these components percapacitive sensor determine the capacitance change of the RX electrodein response to a proximate fingerprint feature. The relationships alsodetermine the level of uniformity in sensor signals to fingerprintfeatures presented at different angles relative to the RX electrode ofthe capacitive sensor (e.g., the level of anisotropy). In all cases, theTX potential will affect the change in capacitance of the capacitivesensor caused by the fingerprint feature and injected noise will affectthe SNR ratio of the sensor signal. Increasing coverage of the substrateby TX electrodes (e.g., minimizing deletions between TX electrodes) mayincreasingly shield noise from being injected into the sensor signal bycircuit elements opposite the TX electrodes from the RX electrodes.

Thus, different attributes of the TX electrodes, insulating layer,propagating electrodes, RX electrodes and/or overlay material andrelationships (e.g., physical and electrical) between these componentsmay be applied in various combinations, per capacitive sensor, andadjusted to design capacitive sensors that meet targeted sensor signallevels, anisotropy, at acceptable SNR. For example, FIGS. 8-11 show aplan view of various sensor arrays, in accordance with embodiments. InFIGS. 8-11, the TX electrodes may be the same as the TX electrodes 302of FIG. 3. In FIGS. 8 and 9 the RX electrodes may be the same as the RXelectrodes 320 of FIG. 3.

FIG. 8 shows an example sensor array 800 in which the width 842 ofportions of propagating electrodes 840 within the unit cell 860 (e.g.,and the corresponding capacitive sensor) is greater than the width 342of the propagating electrodes 340 within the unit cell 360 of FIG. 3.Other embodiments may include propagating electrodes within the unitcell 860 of various numbers, shapes, and sizes without departing fromthe claimed subject matter. FIG. 9 shows an example sensor array 900 inwhich each unit cell 960 (e.g. and the corresponding capacitive sensor)includes a portion of two propagating electrodes 940 and 942 on oppositesides of an RX electrode 920. In other embodiments, another unit cell ofthe sensor array 900 may include a portion of any number of propagatingelectrodes, of any size or shape, and some unit cells of the sensorarray 900 may not include any portion of propagating electrode.

FIG. 10 shows an example sensor array 1000 in which a unit cell 1060(e.g., and the corresponding capacitive sensor) includes a propagatingelectrode 1040 and a totem pole 1022 style RX electrode 1020. The totempole 1022 increases the fringe capacitance between the edges of the TXelectrode 1002 and the RX electrode 1020 within the unit cell 1060 andalso between the propagating electrodes 1040 and the RX electrode 1020compared to those in the unit cell 360 of FIG. 3. The increased fringecapacitance between the edges of the two may increase capacitancebetween the TX electrode 1020 and the RX electrode 1002 and between theRX electrode 1020 and the propagating electrodes 1040, which improvessensor sensitivity in an embodiment. The totem pole 1022 shape of eachRX electrode 1020 includes a main trace 1024 and primary traces 1026,that branch away from the main trace 1024. The unit cell 1060 is shownto include a portion of main trace 1024 and portions of four primarytraces 1026. It can readily be seen that an RX electrode, a TXelectrode, or a propagating electrode 1040 may include additionalbranching traces (e.g., primary, secondary, tertiary) to furtherincrease fringe capacitance between edges of TX electrodes, RXelectrodes, and propagating electrodes. Of course, a sensor array mayinclude, in combination with propagating electrodes, other types of RXelectrode, TX electrode, propagating electrode patterns (e.g.,interleaving and/or interdigitated) that increase fringe capacitancebetween electrode edges to improve capacitive sensor sensitivity andSNR.

For example, FIG. 11 shows an example sensor array 1100 in which a unitcell 1160 (e.g., and the corresponding capacitive sensor) includes apropagating electrode 1140 and an RX electrode 1120 including two maintraces 1122 and 1124, which are conductively coupled and measured as asingle RX electrode. As with the totem pole pattern 1022 of FIG. 10, thetwo main traces 1122 and 1124 provide increased fringe capacitance atthe edges of the RX electrode in the unit cell 1160. In this embodiment,for the propagating electrode 1140 within the unit cell 1160, the entirearea of the propagating electrode 1140 (e.g., as shown in the plan view)is within the area of the unit cell 1160 and within the area of the TXelectrode 1102.

FIG. 12 is a block diagram illustrating one embodiment of an electronicsystem 1200 including a processing device 1210 that may be configured togenerate a fingerprint image. The electronic system 1200 may includes afingerprint module 1216 (e.g., the fingerprint module 104 of FIG. 1)coupled to the processing device 1210 and a host 1250. In oneembodiment, the fingerprint module 1216 is a two-dimensional interfacethat uses the sensor array 1221 to detect fingerprints on the surface ofthe fingerprint module 1216. In various embodiments, the sensor array1221 may include sensor array 300 of FIG. 3, the sensor array 800 ofFIG. 8, the sensor array 900 of FIG. 9, the sensor array 1000 of FIG.10, the sensor array 1100 of FIG. 11, or any other sensor array inaccordance with the embodiments described herein.

In one embodiment, the sensor array 1221 includes sensor electrodes121(1)-121(N) (where N is a positive integer) that are disposed as atwo-dimensional matrix (also referred to as an XY matrix). The sensorarray 1221 is coupled to pins 113(1)-113(N) of the processing device1210 via one or more analog buses 1215 transporting multiple signals.The propagating electrodes (not shown) described herein may be disposedin the sensor array.

The capacitance sensor 1201 may include conversion circuitry to converta capacitance into a measured value. The capacitance sensor 1201 mayalso include a counter or timer circuitry to measure the output of theconversion circuitry. The processing device 1210 may further includesoftware components to convert the count value (e.g., capacitance value)into a sensor electrode detection decision (also referred to as switchdetection decision) or relative magnitude. It should be noted that thereare various known methods for measuring capacitance, such as currentversus voltage phase shift measurement, resistor-capacitor chargetiming, capacitive bridge divider, charge transfer, successiveapproximation, sigma-delta modulators, charge-accumulation circuits,field effect, mutual capacitance, frequency shift, or other capacitancemeasurement algorithms. It should be noted however, instead ofevaluating the raw counts relative to a threshold, the capacitancesensor 1201 may be evaluating other measurements to determine the userinteraction. For example, in the capacitance sensor 1201 having asigma-delta modulator, the capacitance sensor 1201 is evaluating theratio of pulse widths of the output, instead of the raw counts beingover or under a certain threshold.

In one embodiment, the processing device 1210 further includesprocessing logic 1202. Operations of the processing logic 1202 may beimplemented in firmware; alternatively, it may be implemented inhardware or software. The processing logic 1202 may receive signals fromthe capacitance sensor 1201, and determine the state of the sensor array1221, such as whether an object (e.g., a finger) is detected on or inproximity to the sensor array 1221 (e.g., determining the presence ofthe finger), tracking the motion of the object, detecting features(e.g., fingerprint ridges and valleys) based on the received signals, orother information related to an object detected at the fingerprintmodule 1216.

In another embodiment, instead of performing the operations of theprocessing logic 1202 in the processing device 1210, the processingdevice 1210 may send the raw data or partially-processed data to thehost 1250. The host 1250 may include decision logic 1251 that performssome or all of the operations of the processing logic 1202. Operationsof the decision logic 1251 may be implemented in firmware, hardware,software, or a combination thereof. The host 1250 may include ahigh-level Application Programming Interface (API) in applications 1252that perform routines on the received data, such as compensating forsensitivity differences, other compensation algorithms, baseline updateroutines, start-up and/or initialization routines, interpolationoperations, or scaling operations. The operations described with respectto the processing logic 1202 may be implemented in the decision logic1251, the applications 1252, or in other hardware, software, and/orfirmware external to the processing device 1210. In some otherembodiments, the processing device 1210 is the host 1250.

In another embodiment, the processing device 1210 may also include anon-sensing actions block 1203. This block 1203 may be used to processand/or receive/transmit data to and from the host 1250. For example,additional components may be implemented to operate with the processingdevice 1210 along with the sensor array 1221 (e.g., keyboard, keypad,mouse, trackball, LEDs, displays, or other peripheral devices).

The processing device 1210 may reside on a common carrier substrate suchas, for example, an integrated circuit (IC) die substrate, or amulti-chip module substrate. Alternatively, the components of theprocessing device 1210 may be one or more separate integrated circuitsand/or discrete components. In one embodiment, the processing device1210 may be the Programmable System on a Chip (PSoC™) processing device,developed by Cypress Semiconductor Corporation, San Jose, Calif.Alternatively, the processing device 1210 may be one or more otherprocessing devices known by those of ordinary skill in the art, such asa microprocessor or central processing unit, a controller,special-purpose processor, digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), or other programmable device. In an alternativeembodiment, for example, the processing device 1210 may be a networkprocessor having multiple processors including a core unit and multiplemicro-engines. Additionally, the processing device 1210 may include anycombination of general-purpose processing device(s) and special-purposeprocessing device(s).

In one embodiment, the electronic system 1200 is implemented in a devicethat includes the fingerprint module 1216 as part of the user interface,such as in handheld electronics, portable telephones, cellulartelephones, notebook computers, personal computers, personal dataassistants (PDAs), kiosks, keyboards, televisions, remote controls,monitors, handheld multi-media devices, handheld video players, gamingdevices, control panels of a household or industrial appliances, orother computer peripheral or input devices. Alternatively, theelectronic system 1200 may be used in other types of devices. It shouldbe noted that the components of electronic system 1200 may include allthe components described above. Alternatively, electronic system 1200may include only some of the components described above, or includeadditional components not listed herein.

FIG. 13 is a block diagram illustrating one embodiment of a sensor array1321 and a capacitance sensor 1301 that converts changes in measuredcapacitances to a fingerprint image. In various embodiments, the sensorarray 1321 may include sensor array 300 of FIG. 3, the sensor array 800of FIG. 8, the sensor array 900 of FIG. 9, the sensor array 1000 of FIG.10, the sensor array 1100 of FIG. 11, or any other sensor array inaccordance with the embodiments described herein. The fingerprintfeatures are calculated based on changes in measured capacitancesrelative to the capacitances of the same sensor array 1321 in anun-touched state. In one embodiment, sensor array 1321 and capacitancesensor 1301 are implemented in a system such as electronic system 1200.Sensor array 1321 includes a matrix 1325 of N×M electrodes (N RXelectrodes and M TX electrodes), which further includes TX electrodes1322, RX electrodes 1323, and propagating electrodes (not shown) asdescribed in various embodiments herein. Each of the electrodes inmatrix 1325 is connected with capacitance sensing circuit 1301 throughdemultiplexer 1312 and multiplexer 1313.

Capacitance sensor 1301 includes multiplexer control 1311, demultiplexer1312 and multiplexer 1313, clock generator 1314, signal generator 1315,demodulation circuit 1316, and analog to digital converter (ADC) 1317.

The TX and RX electrodes in the electrode matrix 1325 may be arranged sothat each of the TX electrodes overlap and cross each of the RXelectrodes such as to form an array of intersections, while maintaininggalvanic isolation from each other. The propagating electrodes of thesensor array 1321 also are also maintained in galvanic isolation fromthe RX electrodes in some embodiments and bother the RX electrodes andTX electrodes in other embodiments. Thus, each TX electrode and at leaston propagating electrode may be capacitively coupled with each of the RXelectrodes. For example, TX electrode 1322 is capacitively coupled withRX electrode 1323 at the point where TX electrode 1322 and RX electrode1323 overlap.

Signal generator 1314 supplies a clock signal to signal generator 1315,which produces a TX signal 1324 to be supplied to the TX electrodes ofsensor array 1321 array. In one embodiment, the signal generator 1315includes a set of switches that operate according to the clock signalfrom clock generator 1314. The switches may generate a TX signal 1324 byperiodically connecting the output of signal generator 1315 to a firstvoltage and then to a second voltage, wherein said first and secondvoltages are different.

The output of signal generator 1315 is connected with demultiplexer1312, which allows the TX signal 1324 to be applied to any of the M TXelectrodes of sensor array 1321. In one embodiment, multiplexer control1311 controls demultiplexer 1312 so that the TX signal 1324 is appliedto each TX electrode 1322 in a controlled sequence. Demultiplexer 1312may also be used to ground, float, or connect an alternate signal to theother TX electrodes to which the TX signal 1324 is not currently beingapplied. In an embodiment utilizing multiphase TX sensing, different TXsignals may be applied to different subsets of TX electrodes 1322. Forexample, the TX signal 1324 may be presented in a true form to a subsetof the TX electrodes 1322 and in complement or phase-altered form to asecond subset of the TX electrodes 1322, where there is no overlap inmembers of the first and second subset of TX electrodes 1322. Inalternative embodiments, the different TX signals may be unrelated(i.e., not phase-shifted versions of each other).

Because of the electrical coupling between the TX, RX, and propagatingelectrodes, the TX signal 1324 applied to each TX electrode induces acurrent within each of the RX electrodes. For instance, when the TXsignal 1324 is applied to TX electrode 1322 through demultiplexer 1312,the TX signal 1324, in combination with propagating electrodes (notshown) induces an RX signal 1327 on the RX electrodes in matrix 1325.The RX signal 1327 on each of the RX electrodes can then be measured insequence by using multiplexer 1313 to connect each of the N RXelectrodes to demodulation circuit 1316 in sequence.

The mutual capacitance associated with each intersection between a TXelectrode and an RX electrode can be sensed by selecting every availablecombination of TX electrode and an Rx electrode using demultiplexer 1312and multiplexer 1313. To improve performance, multiplexer 1313 may alsobe segmented to allow more than one of the RX electrodes in matrix 1325to be routed to demodulation circuits 1316. In an optimizedconfiguration, wherein there is a 1-to-1 correspondence of instances ofdemodulation circuit 1316 with RX electrodes, multiplexer 1313 may notbe present in the system.

When a finger is in contact with the electrode matrix 1325, thedifferent fingerprint features may cause different changes in themeasured mutual capacitances between the electrodes. For example, afingerprint ridge near the intersection of TX electrode 1322 and RXelectrode 1323 will decrease the charge coupled between electrodes 1322and 1323 by a greater amount than a valley at the same location. Thus,the locations of fingerprint ridges and valleys on the sensor can bedetermined by identifying RX electrodes having a decrease in measuredmutual capacitance in addition to identifying the TX electrode at whichthe corresponding TX signal 1324 was applied. By determining the mutualcapacitances associated with each intersection of electrodes in thematrix 1325, the locations of fingerprint features may be determined.The determination may be sequential, in parallel, or may occur morefrequently at commonly used electrodes. The induced RX signal 1327 isintegrated by demodulation circuit 1316. The rectified current output bydemodulation circuit 1316 can then be filtered and converted to adigital code by ADC 1317, which can then be used by the processing logic1302 to generate the fingerprint image.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described embodiments (or one ormore aspects thereof) may be used in combination with each other. Otherembodiments will be apparent to those of skill in the art upon reviewingthe above description. In this document, the terms “a” or “an” are used,as is common in patent documents, to include one or more than one. Inthis document, the term “or” is used to refer to a nonexclusive or, suchthat “A or B” includes “A but not B,” “B but not A,” and “A and B,”unless otherwise indicated. In the event of inconsistent usages betweenthis document and those documents so incorporated by reference, theusage in the incorporated reference(s) should be consideredsupplementary to that of this document; for irreconcilableinconsistencies, the usage in this document supersedes the usage in anyincorporated references.

Although the claimed subject matter has been described with reference tospecific embodiments, it will be evident that various modifications andchanges may be made to these embodiments without departing from thebroader spirit and scope of what is claimed. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense. The scope of the claims should be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. In the appended claims,the terms “including” and “in which” are used as the plain-Englishequivalents of the respective terms “comprising” and “wherein.” Also, inthe following claims, the terms “including” and “comprising” areopen-ended; a system, device, article, or process that includes elementsin addition to those listed after such a term in a claim are stilldeemed to fall within the scope of that claim. Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels and are not intended to impose numericalrequirements on their objects.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims.

What is claimed is:
 1. A fingerprint sensor array, comprising: aplurality of first electrodes disposed in a first layer, wherein theplurality of first electrodes is arranged according to a pitch of thefirst electrodes; a plurality of second electrodes disposed in a secondlayer, wherein each second electrode crosses each first electrode toprovide a pattern of non-overlapping sensor areas wherein eachnon-overlapping sensor area is associated with a different crossing; anda plurality of propagating electrodes disposed in the second layer,wherein each non-overlapping sensing area includes a portion of at leastone propagating electrode, and wherein each of the plurality of secondelectrodes is galvanically isolated from the plurality of firstelectrodes and the plurality of propagating electrodes.
 2. Thefingerprint sensor array of claim 1, wherein one or more of theplurality of propagating electrodes is coupled to a first electrode, ofthe plurality of first electrodes, through a conductive member.
 3. Thefingerprint sensor array of claim 1, wherein one or more of theplurality of propagating electrodes is capacitively coupled to a firstelectrode, of the plurality of first electrodes, through a dielectricmaterial.
 4. The fingerprint sensor array of claim 1, wherein eachnon-overlapping sensor area includes at least a portion of a firstpropagating electrode and at least a portion of a second propagationelectrode, wherein a portion of each second electrode within each sensorarea is disposed between at least the portion of the first propagatingelectrode and at least the portion of the second propagating electrode.5. The fingerprint sensor array of claim 1, wherein a first group ofpropagating electrodes, of the plurality of propagating electrodes, isassociated with a first electrode, of the plurality of first electrodes,wherein each propagating electrode of the first group is aligned withanother propagating electrode of the first group, along an axis of thefirst electrode.
 6. The fingerprint sensor array of claim 1, wherein awidth of each first electrode is greater than half the pitch of thefirst electrodes.
 7. The fingerprint sensor array of claim 1, wherein awidth of each third electrode is less than half the pitch of the secondelectrodes.
 8. The fingerprint sensor array of claim 1, wherein a widthof each third electrode is the same as a width of at least one of thesecond plurality of electrodes.
 9. The fingerprint sensor array of claim1, wherein a width of each first electrode is greater than half thepitch of the first electrodes.
 10. The fingerprint sensor array of claim1, wherein the second electrode of at least one of the sensor areascomprises a main trace and a primary trace that branches away from themain trace, wherein the sensor area includes at least a portion of theprimary trace.
 11. The fingerprint sensor array of claim 1, wherein thesecond electrode of at least one of the sensor areas comprises aplurality of main traces.
 12. A method comprising: driving one or moretransmit signals on a plurality of first electrodes disposed in a firstlayer and a plurality of propagating electrodes disposed in a secondlayer; and measuring a capacitance of each of a plurality of sensorsthrough a plurality of second electrodes, wherein each second electrodecrosses each first electrode to provide a plurality of discrete sensors,wherein each discrete sensor includes a portion of at least onepropagating electrode, and wherein each of the plurality of secondelectrodes is galvanically isolated from the plurality of firstelectrodes and the plurality of propagating electrodes.
 13. The methodof claim 12, wherein the driving of the one or more transmit signals onthe plurality of propagating electrodes comprises conductively couplingto the propagating electrodes.
 14. The method of claim 12, wherein thedriving of the one or more transmit signals on the plurality ofpropagating electrodes comprises capacitively coupling to thepropagating electrodes.
 15. A system comprising: a fingerprint modulecomprising transmit electrodes disposed in a first layer, receiveelectrodes disposed in a second layer and propagating electrodesdisposed in the second layer, wherein each receive electrode crosseseach transmit electrode to provide a plurality of discrete sensor areas,each discrete sensor area associated with a different crossing andcomprising a portion of at least one propagating electrode; aninsulating material disposed between the first layer and the secondlayer; an overlay material disposed above the second layer; and aprocessing device coupled to the fingerprint module to drive thetransmit electrodes and provide fingerprint data based on sensor signalsreceived through the receive electrodes.
 16. The system of claim 15,wherein the receive electrode of at least one of the discrete sensorareas comprises a main trace and a primary trace that branches away fromthe main trace, wherein the at least one discrete sensor area includesat least a portion of the primary trace.
 17. The system of claim 15,wherein the receive electrode of at least one of the discrete sensorareas comprises a plurality of main traces.
 18. The system of claim 15,wherein the overlay material is between 100 um and 250 um thick.
 19. Thesystem of claim 15, wherein a width of each transmit electrode is widerthan half a pitch of the discrete sensor areas.
 20. The system of claim15, wherein each transmit electrode is between 20 um and 65 um wide andeach receive electrode is between Sum and 15 um wide.